It is known to provide a system for making a recommendation to refuel a vehicle according to the past refueling history of the vehicle driver. See JPH11-37766A, for instance. According to this known system, the remaining amounts of fuel at the time of the most recent five instances of refueling are stored, and the values of these remaining amounts are averaged. When the current fuel level falls below this averaged value, the system notifies the vehicle driver that the time has come for refueling by using synthesized speech. Because the timing of refueling is based on the past history of the vehicle driver, the preference of the vehicle driver is taken into account in determining the timing of issuing a recommendation.
However, because the timing is computed from the amounts of fuel remaining in the fuel tank when the refueling has actually taken place, and the timing of actual refueling is inevitably delayed from the time point of receiving the recommendation, the timing of recommendation tends to be progressively delayed over time. In other words, when the vehicle operator refuels the vehicle in response to a recommendation, owing to the inevitable delay in reaching the gas station, the remaining amount of fuel at the time of refueling is less than the remaining amount of fuel that triggered the recommendation. As this delay accumulates over time, the timing of refueling recommendation may be delayed eventually well beyond the liking of the vehicle driver. This problem is particularly acute when the vehicle is operated in an area where gas stations are not numerous.